1. Field of the Invention
The present invention relates to an apparatus and method for use in a wireless communication system, and more particularly, to an apparatus and method for selecting a processor clock speed and a wireless network.
2. Discussion of the Related Art
Network Selection
Studies have actively been conducted on selection of a wireless network through which data is to be transmitted or determination as to whether to wait for a better network by delay tolerance, when a User Equipment (UE) transmits data to a server in a heterogeneous network environment. Particularly, a study revealed that delay tolerance can improve performance in terms of network capacity or energy due to trade-off. In application of delay tolerance to offloading, if a UE cannot immediately access a Wireless Fidelity (Wi-Fi) network for a specific application insensitive to delay, such as synchronization or transmission of a large file, the UE may enter a Wi-Fi access area by mobility after an allowed delay without data transmission and then may transmit data through the Wi-Fi network. This operation is called delayed offloading, which is a recent extensive research area.
Dynamic Voltage Scaling and Frequency Scaling (DVFS) in Smartphone
Owing to the rapidly increased performance of recent smartphones, the maximum clock speed of a Central Processing Unit (CPU) is increasing significantly. However, most of applications do not require a maximum CPU clock speed. Therefore, recent smartphone chipsets save power by controlling a CPU clock according to a UE load or an application type. Power consumption is calculated based on a CPU clock frequency and a supply voltage by P=αV2f+Leakage power (α is a modeling constant for components other than power and voltage, V is the supply voltage, and f is the CPU clock frequency). Since the supply voltage changes along with the CPU clock in DVFS, a CPU clock-power consumption curve as illustrated in FIG. 1 may be obtained.
However, because most of applications in smartphones are used through a network, there are limitations in determining DVFS based on a CPU load alone. Accordingly, there exists a need for a DVFS scheme taking into account both a network load and a CPU load.